1. Related Field of Art
The present invention concerns a key lock device for use in vehicles and, more in particular, it relates to a key lock device capable of inhibiting unauthorized use of a duplicate or counterfeit key.
2. Description of the Prior Art
Various antitheft devices for automobiles have been proposed so far and it has been known a vehicle key lock device of such a structure as described, for example, in Japanese Patent Publication No. 15141/1992. In the proposed device, coils are provided on both of a key and a key cylinder that is disposed to a vehicle body for operating an ignition switch, and a magnetic circuit is established between both of the coils upon insertion of the key into the key cylinder to transmit and receive electric signals between each of the coils thereby judging whether the inserted key is an authentic one or not.
In this prior art device, when a radiowave signal generated from the coils of the key cylinder is received by coils on the key, it is converted into an electric power to generate a code signal by the electric power. Since the key lock device of such a structure needs no electric cell on the key, the size and the cost of the device can be reduced. However, in the key lock device of the structure described above, it is still desirable that the efficiency of converting the radiowave signal into the electric power is made as high as possible.
Further, in the key lock device of the structure described above, the coils provided on the key are wound around a shaft-shaped core combined between a key shank and a grip portion of the key and put into contact at two positions with an annular core for coils provided on the key cylinder upon insertion of the key into the key cylinder to establish a magnetic circuit. In this structure, since the key shank portion and the grip portion are intervened by the shaft-shaped core, it is difficult to integrally combine the key shank and the grip portion at high strength, and if it is intended to ensure sufficient strength and rigidity for the combined portion, there is a problem that the size of the grip portion is enlarged or the coil assembling work is made troublesome.
Further, in the key lock device of the structure described above, since the intensity of radiowave signals induced by electro-magnetic coupling between the coils greatly depends on a positional accuracy between the key coils and the cylinder coils when the key is inserted into the cylinder lock, it is desirable that an aimed accuracy in assembling the coils can be obtained easily. Furthermore, since the coils and other relevant parts are incorporated in a restricted narrow space, it is desirable that the structure is made as compact as possible.